1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device which is provided with a movable section to be operated on the basis of a displacement action of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device which is capable of detecting displacement of a movable section by the aid of a piezoelectric/electrostrictive element, and a method for producing the same. In particular, the present invention relates to a piezoelectric/electrostrictive device which is excellent in strength, shock resistance, and moisture resistance and which makes it possible to efficiently operate a movable section to a great extent, and a method for producing the same.
2. Background of the Invention
Recently, a displacement element, which makes it possible to adjust the optical path length and the position in an order of submicron, is required, for example, in the fields of the optics, the magnetic recording, and the precision machining. Development is advanced for the displacement element based on the use of the displacement brought about by the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in FIG. 32, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixation section 204, a movable section 206, and a beam section 208 for supporting them which are formed in an integrated manner with a hole 202 provided through a plate-shaped member 200 composed of a piezoelectric/electrostrictive material and with an electrode layer 210 provided on the beam section 208 (see, for example, Japanese Laid-Open Patent Publication No. 10-136665).
The piezoelectric actuator is operated such that when a voltage is applied to the electrode layer 210, the beam section 208 makes expansion and contraction in a direction along a line obtained by connecting the fixation section 204 and the movable section 206 in accordance with the inverse piezoelectric effect or the electrostrictive effect. Therefore, the movable section 206 can perform circular arc-shaped displacement or rotational displacement in the plane of the plate-shaped member 200.
On the other hand, Japanese Laid-Open Patent Publication No. 63-64640 discloses a technique in relation to an actuator based on the use of a bimorph. In this technique, electrodes for the bimorph are provided in a divided manner. The actuator is driven due to the selection of the divided electrodes, and thus the highly accurate positioning is performed at a high speed. This patent document discloses a structure especially in FIG. 4 in which, for example, two bimorphs are used in an opposed manner.
However, the piezoelectric actuator described above involves such a problem that the amount of operation of the movable section is small, because the displacement in the direction of extension and contraction of the piezoelectric/electrostrictive material (i.e., in the in-plane direction of the plate-shaped member) is transmitted to the movable section as it is.
All of the parts of the piezoelectric actuator are made of the piezoelectric/electrostrictive material which is a fragile material having a relatively heavy weight. Therefore, the following problems arise. That is, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Further, the piezoelectric actuator itself is heavy, and its operation tends to be affected by harmful vibrations (for example, residual vibration and noise vibration during high speed operation).
In order to solve the problems described above, it has been suggested that the hole is filled with a filler material having flexibility. However, it is clear that the amount of displacement, which is brought about by the inverse piezoelectric effect or the electrostrictive effect, is decreased even when the filler material is merely used.
On the other hand, the following structure is disclosed in FIG. 4 in Japanese Laid-Open Patent Publication No. 63-64640. That is, in a joined form between a mediating member and a bimorph and between a head and the bimorph, so-called piezoelectric operating sections, both of which cause the strain, extend over respective joined portions. In other words, the bimorph is formed continuously ranging from the mediating member to the head.
As a result, when the bimorph is operated, the displacement action, which is effected with the supporting point of the joined portion between the mediating member and the bimorph, mutually interferes with the displacement action which is effected with the supporting point of the joined point between the head and the bimorph. The expression of the displacement is inhibited. In this structure, it is impossible to obtain such a function that the head is greatly displaced with respect to the external space.
The conventional device of this type involves a problem that in order to displace sufficiently the movable section, a large amount of voltage must be applied.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a piezoelectric/electrostrictive device and a method for producing the same which make it possible to obtain a displacement element that is scarcely affected by harmful vibration during operation and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance, which is liable to cause the displacement in a specific axis direction and can increase the displacement amount of a movable section while keeping a voltage applied to a piezoelectric/electrostrictive element at a low level, as well as a sensor element that makes it possible to detect vibration of the movable section with good accuracy and high sensitivity.
According to the present invention, there is provided a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; wherein at least one thin plate section of the pair of thin plate sections is previously bent in a direction to make mutual approach.
According to another aspect of the present invention, there is provided a piezoelectric/electrostrictive device as described above, wherein the pair of thin plate sections are previously bent in directions to make mutual approach. In this arrangement, it is also preferable that at least one thin plate section of the pair of thin plate sections, or the pair of thin plate sections are previously bent inwardly in convex configurations.
Usually, a thin plate section is bent as a voltage is applied to a piezoelectric/electrostrictive element, whereby a movable section causes displacement. In the present invention, since the pair of thin plate sections are previously bent in directions to make mutual approach and deformed in a direction substantially the same as bending directions of the thin plate sections due to the action of the piezoelectric/electrostrictive element, the thin plate sections are bent by a relatively small force, whereby the movable section causes displacement. Namely, in the present invention, as compared with the conventional piezoelectric/electrostrictive devices, equivalent displacement (displacement in the movable section) can be obtained with a low voltage, whereby an electric power consumption of electronic instruments installed with the piezoelectric/electrostrictive device can be reduced.
Further, the structure in which the thin plate sections are previously bent inwardly in convex configurations is a structure in which not only a high resistance is exhibited against an external force from the width direction of the thin plate section, but also the structure itself is liable to cause displacement in a specific axis direction of each movable section, i.e., in a uniaxial direction along which each thin plate section opposes to the other. Accordingly, this structure has a characteristic that the movable section is hardly rotated in an arc or rotational state, thereby making it possible to displace in an external space to a great extent.
It is preferable that 0 less than xcex4xe2x89xa60.13L is satisfied provided that a bent amount (previously bent amount) of the thin plate section is xcex4, and a length of the thin plate section (distance between the inner walls of the movable section and the fixation section) is L. When the bent amount is set to be within the range described above, the displacement of the piezoelectric/electrostrictive element can be utilized as the displacement of the movable section more efficiently. As a result, the movable section can be displaced to a great extent.
The movable section, the fixation section, and the thin plate section may be made of ceramics or metal. Alternatively, each of the components may be made of a ceramic material, or each of them may be made of a metal material. Further, each of the components may be constructed to have a hybrid structure obtained by combining those produced from materials of ceramics and metal.
In the arrangement described above, it is also preferable that the thin plate section, the movable section, and the fixation section are composed of a ceramic substrate integrated into one unit by simultaneously sintering a ceramic green laminate and cutting off unnecessary portions. It is also preferable that the piezoelectric/electrostrictive element has a film-shaped configuration, and at least any one of the pair of electrodes and/or a piezoelectric/electrostrictive layer is integrated with the ceramic substrate by means of sintering.
In this arrangement, the piezoelectric/electrostrictive element may have a piezoelectric/electrostrictive layer and a pair of electrodes formed on the piezoelectric/electrostrictive layer. It is also preferable that the piezoelectric/electrostrictive element has a piezoelectric/electrostrictive layer and a pair of electrodes formed on both sides of the piezoelectric/electrostrictive layer, and one electrode of the pair of electrodes is formed on at least the thin plate section. In this arrangement, the vibration caused by the piezoelectric/electrostrictive element can be efficiently transmitted via the thin plate section to the movable section or the fixation section. Thus, it is possible to improve the response performance. Especially, it is preferable that the piezoelectric/electrostrictive element is constructed in a stacked form comprising a plurality of the piezoelectric/electrostrictive layers and the electrodes.
When the arrangement as described above is adopted, the following feature is achieved. That is, the generated force of the piezoelectric/electrostrictive element is increased, and thus it is possible to obtain large displacement. Further, it is possible to obtain a high resonance frequency owing to the increase in rigidity of the device itself, making it easy to achieve the high speed of the displacement action. Further, it is also preferable that the hole is filled with a gel material.
According to still another aspect of the present invention, there is provided a method for producing a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; the method comprising the step of cutting off a predetermined portion after forming the piezoelectric/electrostrictive element on at least the thin plate section to produce the piezoelectric/electrostrictive device in which at least one thin plate section of the pair of thin plate sections is bent in a direction to make mutual approach.
According to still another aspect of the present invention, there is provided a production method as described above, comprising the step of cutting off a predetermined portion after forming the piezoelectric/electrostrictive element on at least the thin plate section to produce the piezoelectric/electrostrictive device in which the pair of thin plate sections are previously bent in directions to make mutual approach.
The phrase xe2x80x9cafter producing the piezoelectric/electrostrictive elementxe2x80x9d referred to herein indicates a state in which at least the piezoelectric/electrostrictive layer is formed. As for the electrode to be formed after the formation of the piezoelectric/electrostrictive layer, the electrode may be formed after performing the cutoff.
According to still another aspect of the present invention, there is provided a production method as described above, comprising the steps of integrally sintering a ceramic green laminate including at least a first ceramic green sheet having a window for forming at least the hole thereafter and second ceramic green sheets to be formed into the thin plate sections thereafter to produce a ceramic laminate including portions to be formed into the thin plate sections thereafter denting inwardly; forming the piezoelectric/electrostrictive element on at least an outer surface of a portion of the ceramic laminate to be formed into the thin plate section; and producing a ceramic substrate formed with at least the piezoelectric/electrostrictive element in which the pair of thin plate sections are bent in directions to make mutual approach, by means of at least one time of cutoff treatment for the ceramic laminate formed with the piezoelectric/electrostrictive element. In this process, it is preferable that those having a difference in sintering shrinkage speed and/or sintering shrinkage amount are used for the first and second ceramic green sheets respectively.
It is also preferable that the step of forming the piezoelectric/electrostrictive element is performed in accordance with a film formation method; and any one of a pair of electrodes and/or a piezoelectric/electrostrictive layer is integrated by sintering with at least the outer surface of the portion to be formed into the thin plate section.
According to the production method described above, it is possible to produce effectively and easily a piezoelectric/electrostrictive device capable of displacing a movable section to a great extent while keeping a voltage of a piezoelectric/electrostrictive element at a low level. Also, it is possible to mass-produce the piezoelectric/electrostrictive device having high performance.
According to still another aspect of the present invention, there is provided a method for producing the piezoelectric/electrostrictive device as described above, comprising the steps of integrally sintering a ceramic green laminate including at least a first ceramic green sheet having a window for forming at least the hole thereafter and second ceramic green sheets to be formed into the thin plate sections thereafter to produce a ceramic laminate; forming a precursor of one of a pair of electrodes constituting the piezoelectric/electrostrictive element and/or a piezoelectric/electrostrictive layer on at least an outer surface of a portion of the ceramic laminate to be formed into the thin plate section; sintering the precursor to integrate the ceramic laminate with the precursor and simultaneously denting inwardly a portion to be formed into the thin plate section thereafter; and producing a ceramic substrate formed with at least the piezoelectric/electrostrictive element in which the pair of thin plate sections are bent in directions to make mutual approach, by means of at least one time of cutoff treatment for the ceramic laminate formed.
The step of forming the precursor of one of at least the pair of electrodes constituting the piezoelectric/electrostrictive element and/or piezoelectric/electrostrictive layer may be carried out by a film formation method. In this case, it is preferable that the precursor is formed while controlling a difference in thermal expansion at least between a material for the portion to be formed into the thin plate section and a material of precursor when the precursor is formed on the ceramic laminate.
Accordingly, when the ceramic green laminate and the precursor are sintered, the portion to be formed into the thin plate section thereafter of the ceramic laminate is dented owing to the difference in thermal expansion at least between the material for the portion to be formed into the thin plate section and the material for the precursor, and the piezoelectric/electrostrictive element is consequently formed on the portion to be formed into the thin plate section.
According to still another aspect of the present invention, there is provided a method for producing the piezoelectric/electrostrictive device as described above, preferably comprising the steps of producing a ceramic green laminate including at least a ceramic green sheet having a window for forming at least the hole thereafter and ceramic green sheets to be formed into the thin plate sections thereafter; forming a precursor for constructing at least a part of the piezoelectric/electrostrictive element on at least an outer surface of a portion to be formed into the thin plate section, of the ceramic green laminate; co-firing the ceramic green laminate and the precursor for constructing at least the part or all of the piezoelectric/electrostrictive element so that a ceramic laminate including portions to be formed into the thin plate sections thereafter denting inwardly is produced, and at least the part or all of the piezoelectric/electrostrictive element is formed on at least the outer surface of the portion to be formed into the thin plate section; and producing a ceramic substrate in which the pair of thin plate sections are bent in directions to make mutual approach, by means of at least one time of cutoff treatment for the ceramic laminate.
In this process, it is preferable that the precursor is formed while controlling a difference in thermal expansion at least between a material for the portion to be formed into the thin plate section and a material for the precursor of the piezoelectric/electrostrictive element when the precursor for constructing at least the part of the piezoelectric/electrostrictive element is formed on the ceramic green laminate. Accordingly, when the ceramic green laminate and the precursor for constructing at least the part or all of the piezoelectric/electrostrictive element are sintered, then the portion to be formed into the thin plate section thereafter of the ceramic laminate is dented owing to the difference in thermal expansion at least between the material for the portion to be formed into the thin plate section and the material for the precursor for constructing at least the part of the piezoelectric/electrostrictive element, and the piezoelectric/electrostrictive element is consequently formed on the portion to be formed into the thin plate section.
It is also preferable that the production methods described above further comprise exposing the hole by means of a cutoff treatment for the ceramic laminate in a combined manner.
Therefore, the piezoelectric/electrostrictive device according to the present invention can be utilized as the active device including, for example, various transducers, various actuators, frequency region functional parts (filters), transformers, vibrators, resonators, oscillators, and discriminators for the communication and the power generation, as well as the sensor element for various sensors including, for example, ultrasonic sensors, acceleration sensors, angular velocity sensors, shock sensors, and mass sensors. Especially, the piezoelectric/electrostrictive device according to the present invention can be preferably utilized for various actuators to be used for the mechanism for adjusting the displacement and the positioning and for adjusting the angle for various precision parts such as those of optical instruments and precision mechanical equipments.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.